This isomerization converts glucose which is not very sweet to fructose, the most sweet of the natural sugars. Syrups from this process compete with sucrose (cane sugar) in many food applications. Almost all manufacturers of soft drinks use high fructose syrups because they are less expensive than sucrose. This was devastating to world prices of cane sugar and crippled the economies of some countries.
The isomerization of glucose to fructose is part of the glycolysis cycle that converts glucose to pyruvate. The way this is done is to isomerize the aldehyde (hemiacetal) glucose to the ketone (as a hemiacetal) fructose,and make another phosphate ester. The isomerization takes advantage of the ease of breakage of a C-H bond which involves a carbon next to a carbonyl carbon. This is important in the next step which cleaves the bond between carbons three and four of fructose. It is noted that this bond involves the carbon next to the carbonyl carbon of fructose. This cleavage would not have been possible without the isomerization of glucose to fructose, because the carbonyl group of glucose is too far from carbons three and four to make that bond breakable